The USS Missouri, a Virginia-class attack submarine, entered a key naval base in the southern port city of Busan on Sunday, located 320 kilometres (199 miles) from Seoul, Yonhap News reported, citing the South Korean navy.

"With the deployment of the USS Missouri, we plan to strengthen naval exchanges and cooperation with the United States and to bolster our combined defense posture," the navy said in a statement.

The move comes just three weeks after the USS Santa Fe (SSN-763), a Los Angeles-class submarine, entered the Jeju Naval Base on the southern resort island.

Earlier this week, Seoul, at a South Korea-US security meeting in Washington, raised the possibility of North Korea launching an ICBM in December.

Pyongyang last test-fired a Hwasong-18 solid-fuel ICBM in July.